Arsenic, a known human carcinogen, is also linked to increased atherosclerosis, at lower doses than those associated with carcinogenesis. Although the mechanism by which arsenic causes atherosclerosis is unclear, we have shown in vitro that arsenic inhibits the function of a family of nuclear receptors, including a key regulator of cholesterol homeostasis. The liver X receptor (LXR)/retinoid X receptor (RXR) heterodimer regulates transcription of genes involved in reverse cholesterol efflux to remove lipid from macrophages, and its inhibition has been shown to increase atherosclerotic lesion formation. Our preliminary data lead to the hypothesis that decreased LXR function mediates arsenic-induced atherosclerosis. In Specific aim 1, we will confirm a role for arsenic-induced stress signaling and RXR phosphorylation in inhibition of LXR/RXR transcriptional activity as we have shown for other nuclear receptors. Also, we will determine the step in transcriptional activation of LXR/RXR that is inhibited by arsenic, examining association with coregulatory molecules, and recruitment of transcriptional machinery. Specific aim 2 includes experiments using long-term, low dose arsenic exposure and primary murine and human macrophages to complement preliminary data in transformed macrophages using higher arsenic concentrations. Specific aim 3 describes in vivo experiments designed to complement and confirm the in vitro experiments. We will investigate effects of environmentally-relevant arsenic doses in murine models of atherosclerosis. At high doses, arsenic exacerbates the development of atherosclerosis in ApoE knock-out mice. Therefore, we will correlate changes in LXR target gene expression with atherosclerotic plaque formation and vascular alterations in this model using lower arsenic concentrations. In addition, we will assess the requirement for LXR expression in the pro-atherogenic effects of low dose arsenic using LXR1/ApoE double knock-out mice. These studies will provide insight into the mechanism by which arsenic promotes cardiovascular disease. PUBLIC HEALTH RELEVANCE: Arsenic is a widespread environmental contaminant and listed as the number one health hazard by the EPA. Those individuals exposed to arsenic in the environment are at a greater risk for developing cardiovascular disease. Therefore, we propose experiments designed to understand how arsenic is linked to the development of atherosclerosis in the hope to identify potential interventions.